Conveyors are commonly comprised of a conveyor belt, having an upper or load surface and a lower or return surface, and are mounted for continuous movement around a return roller positioned at each end of the conveyor. Such conveyors are used to transport a myriad of goods, from finely divided particulate matter such as sand, to large and bulky items such as heavy boxes. The drive system for typical conveyors usually comprises a motor connected to one of the return rollers. Advanced or nonstandard conveyor systems include merge, curve and angle conveyors. The belts of these conveyors follow non-standard paths and are of unusual configuration.
The conveyor belt must be stretched tightly around the return rollers in order for the driven return roller to be able to move the belt along its path. By placing the belt under tension, however, various problems arise. These include the need for stronger belts, the faster deterioration of the belts, and the need to cool the belts because of heat generated at points where the belt turns around the return rollers. The problem of excessive heat and consequent belt deterioration for belts under tension is particularly prevalent in such nonstandard conveyors as merge and curve conveyors.
Developments in conveyor technology have led to a drive system which includes a drive wheel and an idler wheel mounted for rotation on spaced apart axes to define a nip which engages the conveyor belt (usually the return portion of the belt) to pull the belt along its path. By driving the belt between the nip of the two wheels, the belt need not be operated under the same degree of tension as in a system in which the driving force is supplied by a return roller. This nip drive system need not be positioned at the ends of the conveyor, but can be positioned any place along the path of travel of the belt.
The nip driving system suffers from the problem that sudden increased loads on the conveyor system can cause the belt to slip rather than be driven through the nip of the two wheels. One improvement in the nip driving system to solve the problem of slip through the nip is to use a spring to bias the drive wheel toward the idler wheel, thereby increasing the pinch on the belt. Also, the drive wheel can be mounted on or supported by one end of an arm which is hinged at the other end for rotation. Rotation of the arm forces the drive wheel toward the idler wheel to increase the pinch on the belt to prevent the belt from slipping though the nip. The axis of the drive wheel, the axis of the idler wheel, and the hinge point of the rotatable arm are configured in such a way that an increase in tension in the belt in the upstream direction or upstream side of the nip pulls on the drive wheel in the upstream direction in a cam-like action to cause rotation of the arm and resulting increase in the pinch of the nip on the belt. This spring/arm support system for a drive wheel can be used successfully to prevent the belt from slipping backwards through the nip when the tension of the belt is suddenly increased. The tension could suddenly increase if a sudden load or increase in load is experienced by the belt.
For various reasons it is desirable to be able to operate conveyor systems as reverse conveyors having belts capable of operating in two directions, i.e., a forward direction and a reverse direction. For example, such a reverse conveyor could be used alternately for loading and for unloading goods. The ability to reverse a conveyor is quite useful in unjamming a jammed conveyor. Further, in complex sorting schemes using multiple conveyors, such as shipping and mail sorting facilities, reversible conveyors enable greater flexibility and efficiency in operation of the system. Conventional conveyors driven by the return rollers are under sufficient tension that they can be reversed. Reversing of these conveyors requires a drive roller on each end. However, low tension conveyor drive wheel spring/arm support systems, which are successful for preventing the belt from slipping backwards upon a sudden increase in tension in the belt, cannot be used on a reversible conveyor since the system is designed for preventing slip in one direction only.
It would be advantageous to be able to provide a conveyor drive system which can operate at low belt tension and yet is capable of being operated in two directions. Such a system should successfully prevent the belt from slipping backwards through the nip when the tension of the belt is suddenly increased. Also, such a system should be able to drive such non-standard conveyors as merges, curves and angle conveyors.